Hydraulic pumps



D. F. MOWBRAY HYDRAULIC PUMPS Sgpt. '5, 1967 Filed May 25, 1965 UnitedStates Patent O 3,339,489 HYDRAULIC PUMPS Dorian Farrer Mowbray,Solihull, England, assignor to Joseph Lucas (Industries) Limited,Birmingham, England Filed May 25, 1965, Ser. No. 458,531 3 Claims. (Cl.103-38) ABSTRACT OF THE DISCLOSURE This invention relates to hydraulicpumps of the kind comprising a body in which is mounted a rotor, therotor having a plurality of angularly spaced bores in which are disposedrespective plungers, an inlet passage and an outlet passage forhydraulic fluid in the body, an angularly adjustable swash plate mountedin the body, against which ends of the plungers, extending from thebores, abut, means for rotating the rotor so that the plungers are movedin the bores by contact of their ends with the swash plate, and a servomechanism for varying theangle of the swash plate in accordance with thepressure of fluid in the outlet passage.

The object of the present invention is to provide an hydraulic pump ofthe kind specified, in a convenient form.

According to the present invention, an hydraulic pump of the kindspecified is characterised by a servo mechanism comprising a piston in acylinder, the cylinder at one side of the piston being in communicationwith the outlet passage from the pump, a spring acting between theopposite side of the piston and a further piston in the cylinder, and avalve, the position of which is dependent upon pressure conditions inthe pump outlet passage, said valve being arranged to control the supplyof fluid to, or the escape of fluid from the end of the cylinderadjacent to the side of said further piston remote from the spring.

A specific example of the invention will now be described with referenceto the accompanying drawings, the single figure of which shows anhydraulic pump in crosssection and incorporating the present invention.

In this example the hydraulic pump has a hollow body in which is mountedfor rotation a rotor 11 having a plurality of angularly spaced borescontaining respective plungers 12. The ends of the plungers 12 protrudefrom the rotor 11 and abut against an angularly adjustable andnon-rotatable swash plate 13. A driving shaft 14 is connected to therotor 11 and as the rotor rotates, fluid is admitted to those bores inthe rotor 11 in which the plungers 12 are moving outwardly and fluid ispumped out of those bores in which the plungers 12 are moving inwardly,through respective inlet and outlet passages 15 and 16 in the body. I

The inlet passage 15 includes a chamber containing a boost pump 17 ofthe impeller type, this pump being driven by the driving shaft 14through gears 18, 19. The outlet passage 16 includes a non-return valve20 and the inlet and outlet passages 15 and 16 are connected through apassage 21 containing an adjustable relief valve 22 oper ative in theevent of excessive pressure conditions in the outlet passage 16.

Connected to the swash plate 13 for moving it angularly to vary thestrokes of the plungers 12, is a servo mechanism comprising a rod 23carrying at its end remote from the swash plate 13, a servo piston 24slidable in a cylinder 25, this cylinder, at its end through which therod 23 extends, being in communication with the pump outlet passage 16through an intermediate chamber 26. This intermediate chamber includes aflow-restricting orifice 27, through which fluid is constrained to passfrom the outlet passage 16 to the cylinder 25, and also a spring loadednon-return valve 28 through which fluid can only pass from the cylinder25 to the outlet passage 16. With this arrangement, response of theservo piston to increasing pressure in the outlet passage is retardedwhilst substantially unrestricted response to decreasing outlet pressurecan take place when the differential pressure across the non-returnvalve 28 has been exceeded. This tends to minimise movement of thepiston 24 in response to relatively small pressure fluctuations.

On the opposite side of the servo piston 24 from the end of the cylinder25 in communication with the outlet passage, is a compression spring 29which, at its other end, abuts against a further piston 30 slidable inthe cylinder 25. The end of the cylinder at the side of the piston 30remote from the spring is in communication with a passage 31 leading toa spool valve 32.

This valve is mounted in a bore in the body 10 and is rotatable by meansof a coaxial cup-shaped and axially adjustable member 32 which is driventhrough gearing 34 from the driving shaft 14 of the pump. Transmissionof the drive between the spool valve 32 and the cup-shaped member 33 isby means of an intervening compression spring 35. Axial adjustment ofthe cup-shaped member 33 determines the spring pressure exerted on thespool valve 32, the opposite end of which is in communication with theoutput passage 16 of the pump through a passage 36. Adjustment thusdetermines the pressure in the outlet passage 16 at which the spoolvalve 32 can move. From the bore in which the spool valve 32 is disposedis a passage 37 axially spaced from the passage 31, which communicateswith the inlet passage 15. Opposite ends of the bore for the spool valve32 communicate through a passage 38 in the body 10.

When the pump is running at a steady rate, the pressure in the outletpassage 16 is at a predetermined value, dependent upon the adjustedposition of the cup-shaped member 33. In this condition, the spool valve32, which has three lands, is so positioned that the central land closesaccess to the passage 31 to the appropriate end of the cylinder 25 ofthe servo mechanism. The two spaces between the three lands of the spoolvalve 32 are respectively in communication with the passages 37 and 38and thus with the outlet passage 16 in one case, and the space nearestto the cup-shaped member 33 being in communication with the outletpassage 16 through the passage 38.

In the event of a decrease in pressure in the outlet passage 16, due,for example, to a demand for fluid by a machine to which the pumpsupplies fluid, the fluid at the end of the servo mechanism cylinder 25which is in communication with the outlet passage 16 escapes when thepressure diiference across the non-return valve 28 exceeds the rating ofits spring. The compression spring 29 of the servo mechanism moves theservo piston 24in a direction to increase the inclination of the swashplate 13 thus increasing the strokes of the plungers 12 in the rotor 11and increasing the supply of fluid to the machine. On the other hand, ifthe pressure increases in the pump outlet passage 16 the servo piston 24is moved against the spring 29 to decrease the strokes of the plungers12 in the rotor 11.

In order that the response of the servo mechanism to changes in pressureshall, as far as possible, be independent of variation in load upon theservo mechanism compression spring 29, the further piston 30, againstwhich this spring 29 acts, is capable of being moved in the followingmanner. During initial movement of the servo piston 24 against thespring 29, the passage 31 to the opposite end of the cylinder 25 isclosed and the fluid which is trapped in this end prevents movement ofthe further piston 30.

However, changes in pressure in the outlet passage 16 are also felt atthe end of the spool valve 32, causing it to move. An increase in thepressure at the outlet passage 16 result in exhausting of the cylinder25 to the inlet passage 15 of the pump, through the passages 31 and 37,the inlet passage 15 being, of course at a lower pressure than theoutlet passage, thus permitting movement of the further piston 30 torelieve the compressive load on the spring 29. Furthermore, a decreasein the pressure at the outlet passage 16 results in movement of thefurther piston 30 in the same direction as the servo piston 24, thusagain bringing the compressive load on the spring 29 approximately toits original value, before movement of the servo piston.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is:

1. An hydraulic pump comprising a body, a rotor mounted within thebody,'the rotor having a plurality of angularly spaced bores, plungersdisposed in the bores respectively, the body having an inlet and anoutlet for hydraulic fluid, an angularly adjustable swash plate mountedin the body against which the ends of the plungers abut, means forrotating the rotor so that as the plungers reciprocate by contact withthe swash plate, liquid is pumped between the inlet and the outlet and apiston and cylinder type servo mechanism for varying the angle of theswash plate in accordance with the pressure in the outlet, the cylinderat one side of the piston being in communication with the outlet fromthe pump, a spring acting between the opposite side of the piston and afurther piston in the cylinder, and a valve, the position of which isdependent upon pressure conditions in the pump outlet, said valve beingarranged to control fiow of fluid to or from the end of the cylinderadjacent to the side of said further piston remote from the spring.

2. An hydraulic pump according to claim 1 in which the valve is in theform of a spool at one end of which, in use, the pressure in the pumpoutlet is exerted, the valve being biased against the action of saidpressure, and passage means being provided for permitting entry orescape of fluid to or from said end of the cylinder adjacent to the sideof the further piston remote from the spring, in accordance withvariations in pressure in the pump outlet.

3. An hydraulic pump according to claim 1 in which the cylinder portionwhich is in communication with the outlet of the pump is incommunication through a passage which includes a flow restrictingportion and a non-return valve, the latter being arranged only to permitof flow of fluid from the cylinder to the pump outlet, this flowoccurring when the pressure drop across the non-return valve exceeds apredetermined value.

References Cited UNITED STATES PATENTS 2,114,443 4/1938 Foisy 103-1622,523,214 9/1950 Ifield 103-38 X 2,713,312 7/1955 Shaw et al 1031623,213,805 10/1965 Cooper et al 103l62 DONLEY J. STOCKING, PrimaryExaminer.

W. L. FREEH, Assistant Examiner.

1. AN HYDRAULIC PUMP COMPRISING A BODY, A ROTOR MOUNTED WITHIN THE BODY,THE ROTOR HAVING A PLURALITY OF ANGULARLY SPACED BORES, PLUNGERSDISPOSED IN THE BORES RESPECTIVELY, THE BODY HAVING AN INLET AND ANOUTLET FOR HYDRAULIC FLUID, AN ANGULARLY ADJUSTABLE SWASH PLATE MOUNTEDIN THE BODY AGAINST WHICH THE ENDS OF THE PLUNGERS ABUT, MEANS FORROTATING THE ROTOR SO THAT AS THE PLUNGERS RECIPROCATE BY CONTACT WITHTHE SWASH PLATE, LIQUID IS PUMPED BETWEEN THE INLET AND THE OUTLET AND APISTON AND CYLINDER TYPE SERVO MECHANISM FOR VARYING THE ANGLE OF THESWASH PLATE IN ACCORDANCE WITH THE PRESSURE IN THE OUTLET, THE CYLINDERAT ONE SIDE OF THE PISTON BEING IN COMMUNICATION WITH THE OUTLET FROMTHE PUMP, A SPRING ACTING BETWEEN THE OPPOSITE SIDE OF THE PISTON AND AFURTHER PISTON IN THE CYLINDER, AND A VALVE, THE POSITION OF WHICH